Saturday, March 1, 2014

How the journal Nature plays fast & loose with the facts about the "pause" in global warming

The recent paper offering excuse #8 for the "pause" in global warming has an accompanying editorial published in Nature Climate Change which plays fast & loose with the facts to cover-up the implications of the "pause." For example, the editorial mentions the "pause" could affect estimates of "climate sensitivity" to CO2, while conveniently leaving out the pause would suggest decreased climate sensitivity, i.e. less effect from man-made CO2. The editorial also says that for this excuse for the pause to be correct, sea level rise and ocean heat uptake should have accelerated since 2000, but conveniently fails to mention the data shows both have instead decelerated during the 21st century.

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Surface global warming has stalled since around 2000 despite increasing atmospheric CO2. A study finds that recent strengthening of Pacific trade winds has enhanced heat transport from the surface to ocean depths, explaining most of the slowed surface warming.

Despite an increasing concentration of CO2 in the atmosphere, global-mean surface temperature has been quite steady since around the turn of this century. A variety of causes have been proposed for this global warming hiatus1, which fall into two categories. First is a reduction in the top-of-atmosphere radiative imbalance, which could be a result of solar variability, stratospheric water vapour increase, an increase of airborne particles or a reduction in methane emissions to name a few. In the other category, the extra heat absorbed by the climate system is not spent warming the surface but somehow is stored elsewhere, with the ocean a likely candidate. In this issue of Nature Climate Change, Matthew England and co-workers2 report that the strengthening of Pacific trade winds during the past two decades has facilitated heat uptake by the subsurface ocean.

Trade winds — prevailing surface winds blowing westwards over the tropical ocean — drive the underlying ocean circulation. Owing to the Earth's rotation, ocean surface currents turn to the right of the wind direction in the northern hemisphere and to the left in the southern hemisphere. Thus, trade winds induce divergent surface flow along the equator, pumping up cooler subsurface water in the central and eastern Pacific. They also blow warm water to the western Pacific where it piles up, and the resulting east–west pressure gradient sustains equatorward subsurface flow, which brings warmer subtropical water to the equatorial subsurface (at a depth below ~100 m). This system varies with time. When trade winds are stronger, this oceanic overturning circulation effect intensifies, cooling the surface while warming the deeper ocean. The opposite change occurs when trade winds weaken. Moreover, active atmospheric convection shifts concurrently with the sea surface temperature and feeds back to the trade-wind changes.

A natural pattern of decade-to-decade variability called the Pacific Decadal Oscillation (PDO), also known as the Interdecadal Pacific Oscillation, highlights this tropical Pacific feature. The negative phase of the PDO, characterized by cooler equatorial Pacific conditions, charges heat into the subsurface ocean, and vice versa for the positive phase. The PDO was negative from the mid-1940s to 1970s, shifting to the positive phase until the late 1990s before again trending negatively so far this century (see Fig. 1). England and colleagues investigate this recent negative trend with a global ocean model. To constrain the model PDO to follow the observations, they superpose observed trends of surface winds over the Pacific from 1992 to 2011. The result accurately reproduces the active subsurface ocean heat uptake and surface cooling in the equatorial Pacific, even if increasing greenhouse gas concentrations are taken into account. Then they utilize a global ocean–atmosphere climate model forced with CO2 emissions scenarios, again constraining the model PDO in a similar way. Through the atmosphere, the influence of surface cooling spreads out from the equatorial Pacific and cools the global surface, causing the surface warming hiatus as observed3.

Figure 1: Recent surface trends.

Sea surface temperature (shading) from NOAA OISST11 and surface wind velocity (arrows) from ERA interim12. Trends are evaluated with monthly anomalies from January 2001 to October 2013 and scaled to ten-year changes. Note that the trade-wind strengthening resides over the surface cooling in the equatorial Pacific. The surface cooling expands polewards along the American coast while the midlatitudes have warmed in the North and South Pacific, a pattern characterizing the negative phase of the PDO. England and colleagues2 find that the wind changes explain the surface global warming hiatus and enhanced heat uptake by the deeper ocean through the PDO.

Without such constraining procedures, a single simulation of a climate model, if not initialized appropriately, cannot reproduce the observed evolution of internal climate variability because of its chaotic behaviour. Averaging many such unconstrained simulations, initialized with slightly different conditions, filters out internal variability and isolates the externally forced response. All climate models project warming in the equatorial Pacific as a forced response, many with equatorial maxima, and a consensus is emerging that forced global warming weakens trade winds. These findings suggest that the recent negative PDO trend is of internal, natural origin rather than the result of a forced [man-made] response. Yet, an ensemble of model simulations should encompass all possible realizations of internal variability in its spread. However, the observed magnitude of trade-wind strengthening between 1992 and 2011 is far outside the ensemble spread of the 48 simulations examined2. Consequently, the observed global-mean surface temperature trends for the past two decades is lower than all but a few of 117 simulations, which means a very low chance of the current hiatus4. It is inferred that the models underestimate PDO magnitude, or overestimate the trade-wind weakening and equatorial Pacific warming as the forced response. The latter affects estimates of climate sensitivity — the magnitude of global surface warming against a given CO2increase.[decreases climate sensitivity]

Even if the transition to the negative PDO is natural, the question of causation is not addressed by England et al., but is worth examining for decadal climate predictions. Some recently suggested possibilities include the remote influence from Indian Ocean warming5, a phase transition in the Atlantic Multidecadal Oscillation6 and stochastic year-to-year variability of El Niño/La Niña1.

The idea of the PDO influence on hiatus periods is not new. Studies have shown that hiatus events are also found in unconstrained model integrations — but not at the observed timings — and are statistically associated with the negative PDO (and other natural variability modes) and enhanced ocean heat uptake7, 8. The contribution of England et al. is to attribute the current hiatus event to the PDO. But models have limitations. How can we observationally confirm that the Earth is still gaining extra heat and that the heat is stored in the ocean? Satellite measurements do not provide the global net radiative imbalance with high accuracy because there is a small difference between the large incoming and outgoing radiation. Instead, we can use observations of ocean heat content because the ocean absorbs more than 90% of the extra heat. Studies show that the heat content has kept increasing during the current hiatus9, 10. However, the result of England et al. favours a higher-order discrimination: the increase of heat content must be accelerated during the hiatus10[, [actually it decelerated] whereas a slowdown in radiative forcing would lead to deceleration. Such a perturbation in heat-content increase should manifest itself in the rate of sea-level rise due to thermal expansion.[rate of sea level rise since 2000 is steady to decelerating]. The quantification of ocean heat uptake by England et al. provides a basis for such attempts to attribute decadal climate change.

It is satellites and OLR measurements and not me who denies that there is any enhancement of the greenhouse effect from increased CO2 in the atmosphere; I am merely reporting what the data states.By the way the data also shows that CH4 is in a very low energy portion of the Earth’s radiative spectrum already dominated by by water vapour so even a ten fold increase in CH4 will have no detectable effect.For your edification clouds reflect the entire spectrum radiated by the Earth and with 50% variable cloud cover; clouds alone can account for over 90% of the Earth’s greenhouse effect.The water molecule has a permanent dipole moment so it has a rotational mode of interaction with the thermal radiation from the Earth which is affected by the entire radiation spectrum. Water vapour varies from near zero to 4% in the optical path which is sufficient to account for at least 30% of the Earth’s greenhouse effect.Water vapour and clouds can account for 120% of the Earth’s greenhouse effect but sincve there is only 100% of the effect possible clouds and water vapour overlap in effect and combined are capable of producing the entire 100% of the observed greenhouse effect even if there is no CO2 in the atmosphere.When CO2 is added it merely takes over some of the effect already in place from clouds and water vapour with no material change to the overall greenhouse effect.If CO2 doubles from its current level about 0.4°C of the greenhouse effect will be removed from clouds and water vapour and taken over by CO2 with no net change to the overall greenhouse effect of 33°CIf CO2 increases ten fold this transfer of effect away from clouds and water vapour will approach the limit of about 0.66°C but the greenhouse effect will still remain constant.The same holds true for all the other so called “greenhouse gases” (this is not a valid scientific term because none of these gases actually have a detectable effect on the Earth’s thermal radiation spectrum with most operating outside the range of wavelengths radiated by the Earth or in very low energy portions already dominated by water vapour which has both rotational and vibrational modes.)Essentially this entire CAGW issue is complete bunk because it is changes to the incoming energy and not changes to the outgoing energy that drives climate and for the past decade the incoming energy has been dropping which has resulted in the overall cooling trend that started in 2002 and with predictions for solar cycle 25 being even lower than our current solar cycle 24 this cooling is expected to last until at least 2032 and possibly much longer. (If we are at the end of the modern warm period following the Medieval Warm Period, The Roman Optimum, and the Minoan Warm period each of which has been succesively cooler than the previous one as part of the overall cooling trend of the past 5000 years likely leading to the next ice age several thousands of years in the future.This thread is about politics driving science which is what the climate change issue is all about